Air-based cooling for data center rack

ABSTRACT

A high-velocity low-pressure cooling system ( 100 ), especially suited for data center applications, includes an air coolant loop ( 102 ), a non-air coolant loop ( 104 ) and a cooler unit ( 126 ) for heat transfer between the loops ( 102  and  104 ). The air loop ( 102 ) is used to chill ambient air that is blown across heat transfer surfaces of equipment mounted in data center racks ( 110 ). In this manner, effective cooling is provided using a coolant that is benign in data center environments.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. 119 to U.S. ProvisionalApplication No. 60/894,844, entitled, “AIR-BASED COOLING FOR DATA CENTERRACK,” filed on Mar. 14, 2007, the contents of which are incorporatedherein as if set forth in full.

FIELD OF INVENTION

The present invention s generally directed to cooling electronicequipment and, in particular, to a cooling system for electricalequipment that uses air as a coolant fluid. The invention has particularutility in the context of cooling rack-mounted electrical equipment suchas in a data center.

BACKGROUND OF THE INVENTION

Certain types of electronic equipment generate considerable heat duringoperation. Cooling such equipment can be problematic, particularly whena number of devices are crowded together in a compact space. The case ofdata centers is illustrative. Certain types of data processing equipmentproduce a large amount of heat in a small form factor. For example,blade servers have multiple heat producing CPUs on boards that slideinto a compact backplane chassis.

Currently, the typical approach to cooling such equipment in a datacenter is via general air conditioning of the data center room using acomputer room air conditioning or “CRAC” unit. However, this is aninefficient means to address hotspots associated with devices, as notedabove, that generate significant heat. In particular, these devicestypically blow cool air into the plenum space beneath the data centerfloor. The cool air is then drawn up through the data center where heatis extracted from the equipment via convection. Even if the coolingcapacity of such a system is increased, e.g., by increasing the volumeof air passed through the data center or further cooling the air, suchsystems are only marginally efficient at addressing such hotspots.

An alternative is water cooling systems that use water or another fluidcoolant. Water cooling was used extensively in data centers in the 1960sthrough the 1980s, especially data centers employing mainframecomputers. Theoretically, such water cooling, or cooling using anothercoolant, could be employed in modern data centers, and some developmenteffort has been initiated in this regard. However, modern data centerstypically employ many network devices and many other data processingperipherals. The result has been an explosion in the amount of datacabling, power conduits and fiber under the data center raised floor.All of this cabling complicates the plumbing that would be required forcooling using conventional coolants. Moreover, modern data centers maybe frequently reconfigured to address changing needs. It will beappreciated that the initial data center configuration and anyreconfiguration may be constrained by plumbing issues and could requirespecialized plumbing service providers in addition to the other serviceproviders employed in such data center projects. In addition, it will beappreciated that any leakage of water from such cooling systems would bepotentially hazardous to personnel and equipment.

SUMMARY OF THE INVENTION

The present invention is directed to a cooling system, especially forrack-mounted electrical equipment, that uses air as a coolant fluid. Thesystem reduces the likelihood of damage to electrical components due toany leakage of the coolant fluid. In addition, novel conduits andconnectors are provided for the cooling system that enables the systemto be easily reconfigured as may be desired to accommodate data centerconfiguration and reconfiguration. Similarly, cooling system capacitycan be easily increased and decreased by adding or removing modularcooling units. Moreover, in one implementation, the system includeschiller units that can be embodied as replacement doors for equipmentracks so as to create and direct chilled air to potential equipmenthotspots.

In accordance with one aspect of the present invention, air is used as acooling fluid in a system for cooling electronic equipment. Theassociated method and apparatus (“utility”) involves providing aclosed-loop coolant circuit and flowing air through the closed-loopcoolant circuit such that the air functions as a coolant fluid. In thisregard, the air used as the coolant fluid can be chilled, e.g., to about−40° F. or about −40° C., for example, by heat exchange with a separatecoolant loop safely separated from the electronic equipment. Heat isthen exchanged between the closed loop coolant circuit and ambient airso as to cool the ambient air, The cooled ambient air can then be flowedacross a heat transfer surface of the electronic equipment to extractheat from the electronic equipment. As noted above, the use of air as acoolant fluid in this regard significantly reduces or substantiallyeliminates the possibility of damage to electronic equipment due to anyleakage of the coolant fluid. The air can be at a relatively lowpressure which simplifies construction, reduces maintenance and enhancesreliability. In order to provide sufficient cooling in such cases, theair may be circulated at a high velocity. Each of these related aspects(low pressure and high velocity) is novel in its own right.

In accordance with another aspect of the present invention, a utilityfor cooling electronic equipment utilizes low-pressure air as aclosed-loop coolant. Specifically, the utility involves providing aclosed-loop coolant circuit, using air as the coolant in the closed-loopcoolant circuit and operating the closed-loop coolant circuit at apressure of no more than about 100 psi. In one implementation, thepressure of the coolant fluid is no more than about 48 psi. The systemallows for simple construction and reconfiguration with reducedmaintenance costs in relation to certain existing cooling systems. In apreferred implementation, a high velocity, low pressure (HVLP) air basedcooling system is provided by combining the high velocity and lowpressure aspects described above.

Thus, in accordance with a further aspect of the present invention, acooling system is provided that circulates air in a closed-loop at ahigh circulation speed. The associated utility involves providing aclosed-loop coolant circuit using air as a coolant in the closed-loopcoolant circuit and operating the closed-loop coolant circuit at acoolant circulation speed of at least about 50 mph. In oneimplementation, the speed of the coolant fluid is between about 75 mphand 90 mph. As noted above, certain advantages are obtained by usinglow-pressure air as a coolant fluid. These advantages can be realizedwhile still providing significant cooling capacity by circulating thecoolant fluid at a high speed.

In accordance with a still further aspect of the present invention, acooling system for cooling electronic equipment in standard equipmentracks is provided that enables cooling capacity to be customized forparticular applications, e.g., configuration and reconfiguration of datacenters. The utility involves a number of cooling modules wherein eachmodule includes a cooling unit with cooling capacity sufficient forcooling more than one, but less than about ten racks. Each modulefurther includes a modular frame adapted to securely interconnect withother modular frames in a number of possible configurations. In thismanner, the cooling capacity can easily be increased or decreased byadding or removing modules. Additionally, the modules can be assembledtogether in different two- or three-dimensional configurations,depending on space requirements/availability.

In accordance with another aspect of the present invention, aspecialized conduit apparatus is provided for use in connection withcooling systems that employ air as a coolant fluid. The conduitapparatus includes an inner conduit defining a passageway for thecoolant air, an outer conduit encompassing the inner conduit and aspacing structure for maintaining spacing between an outer surface ofthe inner conduit and an inner surface of the outer conduit. The spacingbetween the inner and outer conduits accommodates a volume of insulatingair. This spacing could also be used to route wiring for use incontrolling a rack chiller as described below. Alternatively, the outerconduit space can be utilized for the return air path eliminating theneed for a second air conduit. Alternatively, a wiring conduit can befound on an outer surface of the outer conduit for this purpose. Inaddition, an insulating material may be disposed on the outer surface ofthe outer conduit for acoustic and thermal insulation. The noted conduitapparatus allows for circulation of high speed chilled air withoutcondensation fowling on the conduit, as may be desired for variousapplications, including cooling electronic equipment.

In accordance with yet another aspect of the present invention, aspecialized connector apparatus is provided for use in a closed-loop,air based coolant circuit. The connector apparatus includes a pluralityof fingers (which may be formed from plastic, metal or any othersuitable material) that are movable between an open configuration and aclosed configuration. In the open configuration, the fingers areseparated to allow flow of coolant air through a conduit. For example,the fingers may be flush with the conduit wall in the openconfiguration. In the closed configuration, the fingers are drawntogether to substantially prevent flow of the coolant air through theconduit. For example, the fingers, when drawn closed, may form a shapelike, the head of a bullet. The connector apparatus further includes anactuating mechanism for moving the fingers from the closed configurationto the open configuration when the associated closed-loop system isconnected and air is flowing. In this regard, the fingers mayautomatically open in response to air pressure (pressure differential)under these conditions and may automatically close (again, responsive toa pressure change) when a connection is disconnected such that highvelocity air is not discharged into the ambient environment.

In accordance with a further aspect of the present invention, a rackchiller apparatus is provided. The apparatus includes a door structureextending across one side of the rack. The door structure includesventilation openings. The apparatus further includes fans for drawingthe ambient air through the openings of the door and directing the thenchilled ambient air to a heat transfer surface of electronic equipment.A chiller unit associated with the door structure chills the ambient airdrawn through the ventilation openings. For example, door structures maybe provided on both the front and back surfaces (without a chiller unit)of a rack for improving the flow of chilled air thereacross. Differentzones with different target temperatures may be defined within a givenrack. The temperatures may be set by using controls provided for eachzone. For example, on one vertical level of the rack, chiller fans maybe controlled to chill the ambient air before it is blown on the heattransfer surface of the equipment at that level to meet the desiredtarget temperature in that vertical zone. On another level, fans may becontrolled to be idle or maintain a different target temperature. Inaddition, the air leaving the rack (now heated due to heat transfer) maybe chilled to reduce the heat discharged to the room.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and furtheradvantages thereof, reference is now made to the following detaileddescription, taken in conjunction with the drawings in which:

FIG. 1 is a schematic view of an air-based cooling system in accordancewith the present invention;

FIG. 2A is an exploded perspective view of a data center rack with adoor mounted chiller system, with the door cover panels removed forpurposes of illustration, in accordance with the present invention;

FIG. 2B is a front view, partially schematic, of a temperature sensorstrip in accordance with the present invention;

FIG. 2C is a rear view of a data center rack with a vertical power striphaving a temperature sensor strip in accordance with the presentinvention;

FIG. 3A is a cross-sectional view of tubing for an air-based coolingsystem in accordance with the present invention;

FIG. 3B is a side, partially cross-sectional view of a coupling fortubing sections in accordance with the present invention;

FIG. 4A is a side cross-sectional view of a reed valve assemblyincorporated into a tubing section in accordance with the presentinvention;

FIG. 4B is a side view, partially cut-away, of the structure of FIG. 4Awith the reed valve in an open configuration;

FIG. 4C is an end cross-sectional view of he structure of FIG. 4B withthe reed valve in a closed configuration;

FIG. 5 is a side cross-sectional view of an alternative coupling systemfor tubing sections in accordance with the present invention; withmanually reset reed valve integrated.

FIG. 6 illustrates modular cooling unit frames in accordance with thepresent invention;

FIG. 7A is a top plan view of a prior art data center showing a hot andcold raw configuration; and

FIG. 7B shows an air-based cooling system in accordance with analternative implementation of the present invention.

DETAILED DESCRIPTION

In the following description, the invention is set forth in the contextof an air-based cooling system for data center applications. Asdiscussed above, this is a particularly advantageous application of thepresent invention due to, among other things, the crowded cablingenvironment in such contexts, the presence of a number of hotspots anddifferent cooling requirements for different equipment within suchenvironments, the hazards or difficulties associated with water or otherfluid coolants in such environments, and the need for flexibility inconfiguring and reconfiguring equipment in such environments.Nonetheless, it will be appreciated that various aspects of theinvention are applicable in other contexts including other environmentsinvolving electronic equipment. Accordingly, the following descriptionshould be understood as exemplifying the invention and not by way oflimitation.

Referring to FIG. 1, a high-velocity low-pressure (IIVLP) cooling system100 in accordance with the present invention is shown. The system 100generally includes an air coolant loop 102, a non-air coolant loop 104and a cooler unit 126 for heat transfer between the air loop 102 and thenon-air loop 104.

As will be described in more detail below, the air loop 102 is used tochill ambient air that is blown across heat transfer surfaces ofequipment mounted in data center racks 110 as indicated by arrow 116, soas to cool the equipment. In this process, heat is transferred from theambient air to the air loop 102. Accordingly, heat is transferred fromthe air loop 102 to the non-air loop 104 by the cooler unit 126. Thenon-air loop 104, in turn, may either transfer heat directly to outsideair via an outdoor condenser unit, as generally indicated by arrow 106,or may transfer air to a building cooling system (e.g., a water-glycolbased cooling system), which in turn transfers it to the outside air, asindicated by arrow 108. Paths 106 and 108 will thus generally representoptional and alternative implementations of the system 100.

Generally, the final mechanism for transferring heat to outside air, asindicated by arrows 106 and 108, will be existing building facilitiesand are site specific. For example, these elements may include buildingchillers or cooling towers and/or an outdoor condenser unit. The non-airloop 104 may use any appropriate coolant such as Freon. In this regard,the cooler unit 126 may be a conventional unit such as an air-to-Freoncooler unit. As will be understood from the description below, thesystem may be implemented as a number of modular units where each unithas cooling capacity sufficient for only a subset of a typical datacenter environment, e.g., 4-8 racks. Accordingly, the cooler unit 126may be selected to provide heat transfer capacity sufficient for thispurpose. In particular, the cooler unit 126 may be sized to facilitatethe modular functionality of the present invention. Moreover, thecooling units 126 may be packaged into a modular frame as describedbelow.

Loop 102 is a closed-loop that uses air as a coolant. The air in loop102 is maintained at a relatively low pressure, in relation to, forexample, Freon-based systems, but is transmitted within the loop 102 ata fairly high speed. It will be appreciated in this regard that the useof a less dense, lower pressure coolant will generally require that ahigher volume of the coolant be passed across a heat transfer surface inorder to achieve the desired heat transfer effect. It is desirable, inthis application, to maintain the pressure in loop 102 below about 5atmospheres (80 psi) so as to facilitate the modular functionality ofthe invention and associated tubing connections and disconnections. Inthe illustrated embodiment, the air in loop 102 is maintained at about 3atmospheres (48 psi). As discussed above, the use of such a low pressurecoolant generally means that higher coolant speeds will be required toachieve the desired heat transfer capacity. Accordingly, it is desirableto drive the air within loop 102 at a speed in excess of 50 mph fortypical data center applications. In the illustrated embodiment, the airin loop 102 is driven at a speed of between about 75-90 mph.

To achieve the desired air circulation and other air properties, theillustrated loop 102 includes one or more circulation pumps 122 and oneor more air compressor and dryer units 124. The pumps 122 drive the airin the loop 102 at the desired speeds as discussed above. Anyappropriate pumps may be used in this regard. The illustrated pumps 122are spool-type pumps, as commonly used in automobile turbo chargingapplications, except with an electric motor being used as the powersource rather than an exhaust gas stream.

The air compressor and dryer unit 124 dehumidifies the air injected intothe system and pressurizes the air so that the desired air pressurelevel in the closed loop is maintained. In order to achieve the desiredheat transfer effect, the cooler unit 126 maintains the air in the loop102 at a low temperature. The specific temperature depends on a numberof factors including the needs of the particular data centerapplication, ambient temperature and humidity levels and the insulatingproperties of the conduits from which the loop 102 is constructed. Inparticular, it may be desired to control operation of the system 100such that the external surface temperature of the loop 102 is maintainedwithin a controlled temperature band so as to avoid excess condensationthat may be hazardous in a data center environment. For example, it maybe desired to maintain the temperature of the external surface of theloop 102 within a temperature band of about 40° F.-60° F., for example,between about 50° .F-55° F. However, the air within the loop 102 may bemaintained at a considerably colder temperature when an insulatingconduit structure, as will be described below, is employed. In thisregard, the air within the loop 102 may be maintained at temperaturesbelow freezing, for example, about −40° F. The air compressor and dryerunit 124 thus reduces the humidity level of air injected into the loop102, and reduces the humidity level of air introduced into the loop 102due to reconfiguration of the system, so that water does not freeze inthe loop 102.

As shown, the non-air loop 104 and associated components are preferablydisposed outside of the data center 118, for example, in a mechanicalequipment room 120. In this manner, air is the only coolant introducedinto the data center 118 and any leakage of non-air coolants will berestricted to areas outside of the data center 118. The air in the loop102 is used to cool equipment disposed in the racks 110. Generally, thismay be accomplished by using the loop 102 to cool ambient air, which canthen be blown across heat transfer surfaces of the equipment. As theracks 110 are typically organized side-by-side in rows, this cangenerally be most effectively accomplished by blowing the ambient air ina front-to-back or back-to-front direction across the equipment. Theillustrated system blows air from front-to-back as generally indicatedby the arrow 116. This can be done by disposing one or more fans eitherin front of or behind a rack 110 and, for many applications, fansassociated with a chiller on the front side of the racks 110, to coolambient air before it is delivered to the equipment, will be sufficient.In the illustrated embodiment, the front doors of the racks 110 arereplaced with air-to-air chillers with integrated fans 112, and the rearpanels of the racks 110 are replaced with optional air flow boost doorswith integrated fans 114.

This is shown in more detail in FIG. 2A. Specifically, FIG. 2Aillustrates a rack assembly 200, including a front door chiller unit 204(with the front vented cover removed for purposes of illustration) and aback door air flow boost unit 206. Although the assembly 200 is shown inan exploded view in FIG. 2A, it will be appreciated that the front door204 will be disposed on a front surface of the rack 202 and the backdoor unit 206 will be disposed on a rear surface of the rack 202.

The front door unit 204 includes a chiller assembly 214 and a number offans 208, which may be arranged in rows and columns. The chillerassembly 214 includes a number of heat transfer plates 215, that may beconstructed from a heat conductive material such as any of variousmetals, that are chilled by cold air from input conduit 217. The chilledplates 215 extract heat from ambient air that is drawn across the plates215 by fans 208. Alternatively, the fans could be placed in front of thechiller assembly 214 to push air there through. The plates 215, in turn,transfer heat to the coolant air circulated through the conduits 219 ofthe chiller assembly 214. The warmed coolant air is then exhausted tomanifold 221 and, in turn, to the return conduit 223. As will bedescribed below, the input conduit 217 and return conduit 223 may beprovided in the form of coaxial tubing where the cold, supply air flowsthrough the inner conduit and the warmed, return air flows through theouter conduit. This coaxial tubing defines the air coolant loop.

The back door unit 206 in the illustrated embodiment includes a numberof fans 210 disposed in rows and columns similar to the fans 208 of thefront door unit 204. The fans 208 and 210 cooperate to move air acrossthe equipment in the rack 202 generally in the direction indicated byarrow 220. The fans 208 and 210 are preferably sized and positioned soas to provide adequate cooling and also provide the desired differentialcooling for different zones of the rack 202. In the illustratedembodiment, the fans 208 and 210 are approximately 4 inches in diameterand are disposed essentially side-by-side and top-to-bottom across thefull area of the units 204 and 206.

As discussed above, different equipment within a data center and,indeed, different equipment within a single rack 202 may have differentcooling requirements. It is therefore preferable that the fans 208 and210 be operated intelligently. In this regard, a controller 218 allowsfor differential operation of the fans. Preferably, at least the fans indifferent rows of each of the units 204 and 206 may be independentlyoperated. This is because the equipment in the racks 202 are generallyarranged in a vertically stacked configuration. Accordingly, there maybe different cooling needs at different vertical levels of the rack 202.However, if desired, fans in different columns of either unit 204 and206 and/or fans in the front unit 204 and back unit 206 may be operatedindependently. For example, in many cases, it may be unnecessary tooperate any of the fans in the back unit 206 (in many cases, unit 206may be safely omitted). Similarly, fans may be unnecessary in certainrows of the front unit 204 due to the absence of any significant heatgenerating equipment at that location. Optionally, louvers or similarmechanisms (mechanically operable or servo controlled) may be providedin connection with one or more of the conduits 219 so that the coolantair can be directed only to portions of the unit 204 where cooling isrequired.

This intelligent operation of the assembly 200 may be enhanced by theuse of feedback mechanisms in the front 204 and/or back 206 units. Inthe illustrated embodiment, temperature sensors 222 are provided inconnection with the back unit 206 so as to sense the temperature ofambient air exhausted from the rack 202 at different vertical levels(e.g., each fan row) of the rack 202. Such temperature sensors providean indication of the cooling requirements at different vertical levelsof the rack 202. The sensors 222 provide feedback to the controller 218for use in driving the fans 208 and 210 on different rows of the units204 and 206 and, optionally, for controlling flow of the coolant 214. Inthis regard, sensors (not shown) may also be provided in connection withthe front unit 204 to provide temperature differential information foruse in servo control.

FIG. 2B shows an alternative implementation for providing temperaturesensors on the front and/or back door units. Specifically, FIG. 2B showsa sensor strip 230 that may be mounted or otherwise attached to the rackor the door units. The strip 230 may be rigid of flexible, e.g., in theform of a tape that can be rolled for transport and storage and thenunrolled for use. In this regard, the strip 230 can he attached, atleast at end portions 234 thereof, to the rack or door via velcro,screws or other fasteners. The illustrated strip includes a number oftemperature sensors, e.g., diodes 232 with appropriate wiring and logicfor periodically reading the conductivity of the diodes 232. As isknown, conductivity of diodes or changes therein is indicative oftemperature. The strip 230 will generally be mounted with itslongitudinal axis extending vertically on the rack or door.

FIG. 2C shows a still further embodiment for measuring temperatures atdifferent vertical zones of a rack. In this case, the rack 240 has avertical power strip 242 mounted thereto. For example, the power stripmay be a vertical rack mount power strip marketed by Zonit StructuredSolutions. The illustrated power strip 242 has a temperature sensorstrip 244 integrally formed or otherwise mounted thereon. The sensorstrip may be similar in construction and operation to the stripdescribed in FIG. 2B. In any of these embodiments, appropriatecircuiting is provided to return control signals to a servo controlunit.

Referring again to FIG. 1, the system 100 may include a number ofadditional monitoring and servo control elements. With regard to theservo control of the cabinet door cooling units, any appropriatepolicies and rules may be employed to provide the desired cooling, andthese rules may be executed by the controller 128. In this regard, notonly the cooling needs, but also efficiency considerations and any otherappropriate considerations may be taken into account. In the illustratedimplementation, the standard cooling policy for the servo control systemis to try to ensure that all of the air exhausted from the rack is ofequal temperature for each vertical subsection of the rack as measuredby the sensors, which may be, for example, thereto sensor strips, whichtransmit control signals to the controller 128 by appropriate wiringwhich will be discussed in more detail below. If the temperaturemeasured at one section of the rack is hotter than at another section,the fans in the front door unit and back door unit associated with thehotter section may be run faster to provide more airflow and equalizethe exhaust air temperature. This policy can be manually overridden froman LCD screen with control buttons on the front door unit that allowsdifferent vertical zones in the rack (typically at least 4 zones) tohave different targeted exhaust air temperatures. It will be appreciatedthat data center equipment often comes with cooling specifications thatdictate what the maximum exhaust air temperature from the unit should befor adequate cooling. The noted method of cooling management is wellsuited to accommodate such specifications.

The controller 128 also executes a main servo control function for theloop 102. This logic controls the movement of air in the loop 102. Itmonitors and maintains air pressure, humidity and velocity in the closedloop. The illustrated controller 128 thus receives inputs, as generallyindicated by arrow 130, from appropriate pressure, humidity and velocitysensors associated with the loop 102 and provides appropriate controloutputs, as generally indicated by line 132, to the pumps 122 andcompressor and dryer unit 124. The controller 128 may also receivetemperature inputs from the sensors on the rack door units discussedabove so as to provide indication of cooling needs. This informationfrom the rack door units may be fed to the controller 128 via serialwiring and can be used by the controller 128 to adjust the circulationrate in the loop 102.

The illustrated system 100 also includes a power distribution unit 130.The unit 130 provides power to the equipment in the racks 110. Inparticular, the unit 130 may be associated with redundant power sourcesto enable failsafe operation of critical equipment. For example, theunit 130 may be a power distribution unit marketed by Zonit StructuredSolutions. In the illustrated embodiment, the unit 130 includes aprocessor such as a single board computer that can allow for energyconsumption load balancing between the modular units, as will bediscussed in more detail below. In this regard, energy cost is muchlower if it is uniformly consumed rather than having usage characterizedby peaks and valleys. The illustrated unit 130 thus operates as acooling load-leveler and scheduler. It communicates with the main servocontrol of each module and monitors overall cooling status and load. Itthen schedules cooling cycles for each module to optimize energy usagepatterns.

This controller may also communicate with power management logic of theunit 130. In particular, the cooling data history and status can becommunicated to such logic of the unit 130, which can maintain abaseline history that can be viewed via a web interface. The unit 130can also monitor the data center environment based on inputs from thevarious modules. In this manner, isothermal contours and convectionpatterns can be displayed for analysis and further optimization ofsystem operation.

FIG. 3A shows tubing 300 that may be employed in the air coolant loop.The illustrated tubing 300 includes an inner conduit 302 and an outerconduit 304 separated by a space 306. Radial ribs 308 are utilized toprovide the desired spacing. As discussed above, the inner conduit 302may carry the cold supply air to the racks to be cooled and the outerconduit 304 may carry the warmed return air to the cooler unit. It willbe appreciated that electrical wiring may be disposed within the space306 or within a recess provided in the external surface of the tubing ifdesired. Alternatively, electrical wiring may be taped or strapped tothe external surface of the tubing 300. In the illustrated embodiment, aconductive strand 310 is embedded in the wall of the outer conduit 304.This strand 310 can be used, for example, to serially transmit controlsignals to and/or from the temperature sensors or a controller forcontrolling the door fans.

The conduit assembly 300 is designed to carry the cooled air in the aircoolant loop. The assembly 300 provides sufficient insulation inrelation to the inner conduit so that condensation on the outside of theouter conduit is minimized no as to reduce or substantially eliminatewater dripping that may be hazardous in a data center environment, Theassembly 300 also attenuates sound so that the fast moving cooling airdoes not cause excessive noise. The assembly 300 is constructed fromplastic having the desired insulating and sound attenuating propertiesand is extruded into the cross-section shown in FIG. 3A.

FIG. 3B shows a coupling unit 310 for coupling two sections of tubing312 and 314, which may be, for example, tubing having an embeddedconductive trace as discussed above. More specifically, the tubing 312and 314 may be tubing as shown in FIG. 3A used to assemble an aircoolant loop in a data center cooling application, though the couplingunit is applicable in other contexts. The illustrated coupling unit 310is generally in the form of a sleeve having first and second recesses316 and 318 for receiving ends of the tubing 312 and 314. The recessesare formed by walls that have teeth 320 extending radially inwardlytherefrom. When the tubing 312 and 314 is inserted into the recesses 316and 318, the teeth 320 engage and slightly penetrate the outer wall ofthe tubing. The teeth 320 are oriented so as to resist withdrawal of thetubing 312 and 314 from the recesses. 0-rings 322 seal the coupling unit310 to substantially eliminate leakage of air (or other transmittedfluid).

The illustrated coupler also provides electrical coupling of the tubing312 and 314. As noted above, the tubing 312 and 314 has embeddedconductive traces. The teeth 320 have conductive external surfaces sothat the teeth engage the conductive trace when the teeth penetrate theexternal surface of the tubing 312 and 314. In this regard, rows ofteeth in each recess 316 and 318 can be circumferentially offset fromone another such that at least one tooth engages the trace no matterwhat the angular orientation of the tubing 312 or 314 when it isinserted into the recesses 316 and 318. The teeth 320 of the first andsecond recesses 316 and 318 are electrically interconnected by leads324. In this manner, a circuit, e.g., a data center air coolant loop, anbe concomitantly wired as it is plumbed.

The center portion of the illustrated coupling unit 310 includes aninner conduit 326 and an outer conduit 328. The spacing between theseconduits 326 and 328 may be maintained by radial ribs. These conduits326 and 328 allow for efficient interconnection of coaxial tubing asdescribed above.

One advantage of the present invention is that the overall coolingsystem for a data center is provided in a number of modular units. Thisallows data centers to display cooling as needed and expand capacity ata later time. It is desired that such configuration and reconfigurationbe accomplished efficiently without requiring specialized skill.Accordingly, it is desirable that the conduits that make up the aircoolant loop can be easily connected and disconnected, such as bycoupling units as described above. In addition, it is desirable thatairflow automatically be discontinued in the event that a connector isdisconnected so as to avoid the discharge of high-velocity, cold airinto the ambient environment.

FIGS. 4A-4C illustrate a tubing end section 400 to provide the desiredfunctionality. As shown, the end section 400 includes an outer conduit402 and an inner conduit 404, as described above. A reed valvesubassembly 403 is provided at an outlet end 405 of the assembly 400,where the airflow direction is indicated by arrow 411. That is, theoutlet end 405 is at the downstream end of the conduit section when theconduit section is incorporated into an air coolant loop. Theillustrated valve subassembly 403 includes a number of valve fingers 406connected to the inner conduit 404 by a hinge 408, such as an integralfabric (e.g., plastic) hinge. Alternatively, a mechanical hinge could beutilized.

In an open configuration, as shown in FIGS. 4A and 4B, the fingers 406are disposed within a recess formed in the inner conduit 404 so thatthey do not substantially obstruct airflow through the conduit 404. In aclosed configuration, as shown in FIG. 4C, the fingers 406 snap togetherso as to substantially cut-off air flow. Preferably, the valvesubassembly 403 is self-actuating so as to automatically cut-off airflow upon disconnection of a conduit section. That is, when the conduitsection is connected within an air coolant loop and air is flowing, thevalve subassembly 403 will automatically assume the open configurationof FIGS. 4A and 4B. However, when the conduit section is disconnected,the valve subassembly 403 will automatically assume the closedconfiguration of FIG. 4C. In this regard, the valve subassembly 403 maybe biased towards the open configuration, for example, by internalspring force of the hinge material.

As best seen in FIG. 4A, the illustrated fingers 406 have across-section generally shaped like a cambered airfoil. Air flow acrossthe surface of these fingers will draw the fingers radially inwardly.This drawing force will increase when the conduit section isdisconnected. By appropriate design of the hinge, air flow across thefingers 406 when the tubing section is incorporated into an air coolantloop and air is flowing will allow the valve assembly to remain in theopen configuration. However, when the tubing section is disconnected,the air velocity will momentarily increase dramatically, increasing theaerodynamic lift on the “fingers” lifting them into the oncoming airstream. The tips of the fingers will be drawn into the air stream, whichwill then snap the fingers into the closed configuration.

The reed valve subassembly 403 will also automatically reopen when thetubing is connected and air is flowing. In particular, the fingers 406,by design, do not form an air-tight seal in the dosed configuration.Rather, some air will leak between the fingers or through a smallcentral opening due to rounding of the finger tips. Since the coolant isbenign air (though it is cold), this small leakage is not a safetyconcern. This leakage causes the pressure differential across the reedvalve subassembly 403 to reduce until the spring force of the hingeallows the valve subassembly to reopen.

An alternative mechanical actuation mechanism is shown in FIG. 5.Specifically, FIG. 5 shows a connection mechanism 500 involving adownstream male end of a first tubing assembly 502 for connection to anupstream female end of a second tubing assembly 504. As described above,the tubing assemblies 502 and 504 include internal conduits 508 and 512and external conduits 506 and 510. The first tubing assembly 502includes a reed valve subassembly 516. The reed valve subassembly 516 ishingedly connected to the internal conduit 508 and includes lever arms518 that extend through an opening such as a slot formed in the externalconduit 506. The second tubing assembly 504 includes a flanged section514 dimensioned to extend over an end section of the first tubingassembly 502. When the tubing sections 502 and 504 are interconnected,the flanged section 514 depresses the lever arms 518 and opens the reedvalve 516. The reed valve 516 is biased towards a closed position suchthat upon disconnection of the assemblies 502 and 504 the valve assembly516 assumes the closed position as illustrated.

FIG. 6 illustrates how the cooler units of the present invention can beprovided in modular frames to enable any desired two-dimensional orthree-dimensional data center topology. As shown in FIG. 6, the system600 is constructed from a number of modules 601-605. Each of thesemodules may include, for example, an air-to-Freon cooling unit andassociated structure, as described above. The modules 601-605 includeregistration and interconnection elements to enable interconnection ofthe modules in horizontal and/or vertical configurations. In theillustrated embodiment, these registration elements include maleconnectors 606 and female connectors 608 for enabling such connection.Such registration of the modules 601-605 also allows for simpleinterconnection of electrical and pneumatic structures as between themodules 601-605 if desired.

The air-based cooling system of the present invention can be implementedusing chillers other than door mounted units as described above. Inparticular, it may be desired to provide a floor or ceiling mountedchiller to address data center hot spots. In this regard, FIG. 7A showsan example of how a well conceived data center 700 may be configuredtoday. The data center 700 includes racks 702 arranged in rows. Acomputer Room Air Conditioner (CRAC) unit 710 forces cool air into asubfloor plenum space. This cool air (indicated by arrows 706) entersthe data center 700 via vents 704 generally disposed adjacent the racks702. Generally, cool air 706 is blown on the front side of a rack andwarm air (generally indicated by arrows 708) exits the back side of therack.

Adjacent rows of racks are configured so that rack back sides face oneanother and front sides face one another. The effect is to definealternating warm aisles and cold aisles between rack rows. Preferably,CRAC units 710 are positioned at the ends of warm aisles to draw in thewarm air for cooling as shown. However, this preferable configuration isoften not applied. For example, there may not be a CRAC unit 710available. Fore each warm aisle, the result can be hot spots within thedata center 700. Even when a preferable configuration is applied, therecan be local hot spots, especially towards the tops of racks.

FIG. 7B shows a data center 720 employing a chiller unit 722 inaccordance with the present invention. The data center 720 includes rowsof racks 724, a CRAC unit 726, a subfloor plenum 728 and vents 730, allgenerally as described in FIG. 7A. The data center 720 also includes aconventional overhead raceway 732. Because the chiller unit is air-basedand can be constructed of light-weight materials, it an be simply hungfrom the raceway via a bracket 734 or similar mounting hardware. Thechiller unit 722 draws warm air from a warm aisle (thereby reducing theload on the CRAC) and drops cold air down on the rack front. Thisadvantageously delivers cooing to the highest equipment in the rack. Itwill be appreciated, however, that the chiller unit could be floormounted or at another location.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. Furthermore, thedescription is not intended to limit the invention to the form disclosedherein. Consequently, variations and modifications commensurate with theabove teachings, and skill and knowledge of the relevant art, are withinthe scope of the present invention. The embodiments describedhereinabove are further intended to explain best modes known ofpracticing the invention and to enable others skilled in the art toutilize the invention in such, or other embodiments and with variousmodifications required by the particular application(s) or use(s) of thepresent invention. It is intended that the appended claims be construedto include alternative embodiments to the extent permitted by the priorart.

1. A method for use in cooling electronic equipment, comprising:providing a first closed-loop coolant circuit; flowing air through thefirst closed-loop coolant circuit such that the air functions as acoolant fluid; exchanging heat between said first closed-loop coolantcircuit and ambient air so as to cool the ambient air; and flowing thecooled ambient air across a first heat transfer surface of electronicequipment.
 2. A method as set forth in claim 1, further comprising thesteps of providing a second closed loop coolant circuit having a coolantfluid different than that of the first circuit and exchanging heat asbetween the first and second circuits.
 3. A method as set forth in claim1, wherein said stop of exchanging heat comprises using the firstcircuit to cool second heat transfer surfaces and operating at least onefan to move said ambient air across said second heat transfer surfaces.4. A method as set forth in claim 1, wherein said step of flowing aircomprises driving said air in said first circuit at a speed of at least50 mph.
 5. A method as set forth in claim 1, further comprising the stepof pressurizing said air in said first circuit to a pressure greaterthan 1 atm.
 6. A method as set forth in claim 3, wherein said step offlowing comprises disposing said second heat transfer surfaces and saidfan in a door unit of a rack containing said equipment.
 7. An apparatusfor use in cooling electronic equipment, comprising: a first closed-loopcoolant circuit having a heat exchange surface for exchanging heat withambient air; and an air circulator for circulating air through saidfirst closed-loop coolant circuit.
 8. An apparatus as set forth in claim7, further comprising a second closed-loop coolant circuit having asecond coolant fluid different than that of said first circuit.
 9. Anapparatus as set forth in claim 7, wherein said air circulator isoperative for circulating said air in said first circuit at a speedgreater than 50 mph.
 10. An apparatus as set forth in claim 7, furthercomprising an air pressurizer for pressurizing said air in said firstcircuit to a pressure greater than 1 atm.
 11. An apparatus as set forthin claim 7, further comprising at least one fan for moving ambient airacross said heat exchange surfaces.
 12. An apparatus as set forth inclaim 8, wherein said apparatus includes a number of fans that areindividually controllable to provide differential cooling.
 13. Anapparatus as set forth in claim 12, wherein said fans are controlledresponsive to feedback from temperature sensors.
 14. A method for use incooling electronic equipment, comprising: providing a closed-loopcoolant circuit; using a gas phase coolant in said closed-loop coolantcircuit; and operating said closed-loop coolant circuit at a pressure ofno more than about 100 psi and using said gas phase coolant at very lowtemperatures no less than 50° below zero F.
 15. A method as set forth inclaim 14, wherein said closed-loop coolant circuit is operated at apressure of no more than about 48 psi.
 16. A method as set forth inclaim 14, wherein said gas phase coolant is moved at a speed of at leastabout 50 mph in said circuit.
 17. A method for use in cooling electronicequipment, comprising: providing a closed-loop coolant circuit; using agas phase coolant in said closed-loop coolant circuit; and operatingsaid closed-loop coolant circuit at a coolant circulation speed of atleast about 50 mph.
 18. A method as set forth in claim 17, wherein saidclosed-loop coolant circuit is operated at a coolant circulation speedof between about 75-90 mph.
 19. An apparatus for use in coolingelectronic equipment in standard equipment racks, comprising a pluralityof cooling modules wherein each module includes a cooling unit withcooling capacity sufficient for cooling more than 1 but less than about10 racks, and a modular frame, wherein the modular frame of each moduleis adapted to securely interconnect with another of said modular framesin a plurality of possible configurations.
 20. An apparatus as set forthin claim 19, wherein said frames can be interconnected in verticallystacked and horizontally interconnected configurations. 21.-46.(canceled)